Stabilization circuit for junction lasers

Abstract

Described is a stabilization circuit for reducing the sensitivity of a junction laser to variations in the amplitude of drive current pulses. The circuit comprises a transistor connected in common emitter configuration, a junction laser connected between the collector and emitter, a photodetector connected between a voltage node and the emitter, a nonlinear element, such as a switching diode, connected between the node and the base, means for coupling a portion of the laser radiation to the photodetector, and means for coupling an input signal (e.g., current pulses) between the base and emitter. In one embodiment the photodetector is an avalanche photodiode to provide gain and the nonlinear element is a switching diode. In another embodiment the nonlinear element is a switching transistor to provide gain and the photodetector is a PIN photodiode.

What is claimed is: 
     
       1. A stabilization circuit comprising a drive transistor connected in common emitter configuration and having emitter, base and collector electrodes; a junction laser coupled between said collector and emitter electrodes; a photodetector coupled to said emitter electrode; a portion of the radiated output from said laser being coupled to said photodetector; and means for coupling an input signal between said base and emitter electrodes; characterized in that: said photodetector is coupled between a voltage node of said circuit and said emitter electrode; and   a nonlinear rectifying junction element is coupled between said node and said base electrode.   
     
     
       2. The circuit of claim 1 wherein said nonlinear element is a switching diode and said photodetector is a photodiode. 
     
     
       3. The circuit of claim 1 wherein said photodiode is an avalanche photodiode. 
     
     
       4. The circuit of claim 1 wherein said photodetector is a photodiode and said nonlinear element is a control transistor having emitter, base and collector electrodes, its base electrode being coupled to said node, its collector electrode being coupled to said base electrode of said drive transistor and its emitter electrode being coupled to the emitter electrode of said drive transistor.